From 86bc97911c61365ea90603b68fb28e4e4f3b062d Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan@mnt.io>
Date: Thu, 21 May 2026 17:55:35 +0200
Subject: [PATCH] feat(sdk): Allow to reset an `EventFocusedCache`.

This patch updates `ResetCaches` to handle the event-focused caches.
---
 .../event_cache/caches/event_focused/mod.rs   | 31 +++++++++-
 .../matrix-sdk/src/event_cache/caches/mod.rs  | 57 ++++++++++++++++---
 2 files changed, 79 insertions(+), 9 deletions(-)

diff --git a/crates/matrix-sdk/src/event_cache/caches/event_focused/mod.rs b/crates/matrix-sdk/src/event_cache/caches/event_focused/mod.rs
index 5ecccc9a2..2005c2e0c 100644
--- a/crates/matrix-sdk/src/event_cache/caches/event_focused/mod.rs
+++ b/crates/matrix-sdk/src/event_cache/caches/event_focused/mod.rs
@@ -31,6 +31,7 @@
 
 use std::sync::Arc;
 
+use eyeball_im::VectorDiff;
 use matrix_sdk_base::{
     deserialized_responses::TimelineEvent,
     event_cache::{Event, Gap},
@@ -90,7 +91,7 @@ pub(crate) enum EventFocusedPaginationMode {
     },
 }
 
-struct EventFocusedCacheState {
+pub(super) struct EventFocusedCacheState {
     /// The room owning this event-focused cache.
     room: WeakRoom,
 
@@ -503,6 +504,24 @@ impl EventFocusedCacheState {
 
         Ok((result.chunk, result.next_batch_token))
     }
+
+    /// Reset this data structure as if it were brand new.
+    ///
+    /// Return a single diff update that is a clear of all events; as a
+    /// result, the caller may override any pending diff updates
+    /// with the result of this function.
+    pub fn reset(&mut self) -> Result<Vec<VectorDiff<Event>>> {
+        self.chunk.reset();
+        self.propagate_changes();
+
+        let diff_updates = self.chunk.updates_as_vector_diffs();
+
+        // Ensure the contract defined in the doc comment is true:
+        debug_assert_eq!(diff_updates.len(), 1);
+        debug_assert!(matches!(diff_updates[0], VectorDiff::Clear));
+
+        Ok(diff_updates)
+    }
 }
 
 /// A cache for an event-focused timeline.
@@ -543,6 +562,16 @@ impl EventFocusedCache {
         }
     }
 
+    /// Return a reference to the state.
+    pub(super) fn state(&self) -> &Arc<RwLock<EventFocusedCacheState>> {
+        &self.inner
+    }
+
+    /// Get a reference to the _update sender_.
+    pub(super) async fn update_sender(&self) -> EventFocusedCacheUpdateSender {
+        self.inner.read().await.sender.clone()
+    }
+
     /// Subscribe to updates from this event-focused timeline.
     pub async fn subscribe(&self) -> (Vec<Event>, Receiver<TimelineVectorDiffs>) {
         let inner = self.inner.read().await;
diff --git a/crates/matrix-sdk/src/event_cache/caches/mod.rs b/crates/matrix-sdk/src/event_cache/caches/mod.rs
index c4f59f742..277619f37 100644
--- a/crates/matrix-sdk/src/event_cache/caches/mod.rs
+++ b/crates/matrix-sdk/src/event_cache/caches/mod.rs
@@ -430,6 +430,13 @@ pub(super) struct ResetCaches<'c> {
         pinned_events::PinnedEventsCacheStateLockWriteGuard<'c>,
         pinned_events::PinnedEventsCacheUpdateSender,
     )>,
+    event_focused_lock: OwnedRwLockWriteGuard<
+        HashMap<event_focused::EventFocusedCacheKey, event_focused::EventFocusedCache>,
+    >,
+    event_focused_locks: Vec<(
+        OwnedRwLockWriteGuard<event_focused::EventFocusedCacheState>,
+        event_focused::EventFocusedCacheUpdateSender,
+    )>,
 }
 
 impl<'c> ResetCaches<'c> {
@@ -459,11 +466,26 @@ impl<'c> ResetCaches<'c> {
             None
         };
 
-        // TODO (in next commits).
-        let _ = event_focused;
-        todo!();
+        // Acquire an exclusive access to the event-focused caches.
+        // Then, for each event-focused, acquire an exclusive access to its state.
+        let event_focused_lock = event_focused.clone().write_owned().await;
+        let mut event_focused_locks = Vec::new();
 
-        Ok(Self { room_lock, threads_lock, thread_locks, pinned_events_lock })
+        for event_focused in event_focused_lock.values() {
+            event_focused_locks.push((
+                event_focused.state().clone().write_owned().await,
+                event_focused.update_sender().await,
+            ));
+        }
+
+        Ok(Self {
+            room_lock,
+            threads_lock,
+            thread_locks,
+            pinned_events_lock,
+            event_focused_lock,
+            event_focused_locks,
+        })
     }
 
     /// Reset all the event caches, and broadcast the [`TimelineVectorDiffs`].
@@ -473,7 +495,14 @@ impl<'c> ResetCaches<'c> {
     ///
     /// It can fail if resetting an event cache fails.
     pub async fn reset_all(self) -> Result<()> {
-        let Self { room_lock, threads_lock, thread_locks, pinned_events_lock } = self;
+        let Self {
+            room_lock,
+            threads_lock,
+            thread_locks,
+            pinned_events_lock,
+            event_focused_lock,
+            event_focused_locks,
+        } = self;
 
         // Room.
         {
@@ -491,9 +520,7 @@ impl<'c> ResetCaches<'c> {
 
         // Threads.
         {
-            for thread_lock in thread_locks {
-                let (mut thread_state, thread_update_sender) = thread_lock;
-
+            for (mut thread_state, thread_update_sender) in thread_locks {
                 let updates_as_vector_diffs = thread_state.reset().await?;
                 thread_update_sender.send(
                     TimelineVectorDiffs {
@@ -522,6 +549,20 @@ impl<'c> ResetCaches<'c> {
             }
         }
 
+        // Event-focused.
+        {
+            for (mut event_focused_state, event_focused_update_sender) in event_focused_locks {
+                let updates_as_vector_diffs = event_focused_state.reset()?;
+                let _ = event_focused_update_sender.send(TimelineVectorDiffs {
+                    diffs: updates_as_vector_diffs,
+                    origin: EventsOrigin::Cache,
+                });
+            }
+
+            // Now we can release the exclusive access over the event-focused caches.
+            drop(event_focused_lock);
+        }
+
         Ok(())
     }
 }